1. Field of the Invention
The present invention concerns an intake manifold for an internal combustion engine.
2. Description of the Conventional Art
The amount and state of the air flow into the combustion chambers of an engine considerably affects the power, exhaust and fuel consumption rate of the engine. Accordingly it is desirable to reduce the resistance of the intake air flow and to regulate the flow of the intake air to fit the running condition of the engine. One of the methods for increasing the engine efficiency is to cause the intake air to swirl in the combustion chambers. However, this method can not provide a desirable engine efficiency over a wide engine speed range. The U.S. Pat. No. 4,765,286 discloses an intake manifold for an internal combustion engine, which has a selectively controlled variable length flow path whereby the manifold may be resonantly tuned for optimum performance over a wide engine speed range. Although the patent works satisfactorily, the internal structure of the manifold is much complicated to provide the selectively controlled variable length flow path, thereby decreasing the production efficiency thereof.